Telephone systems make use of dial tones to inform the telephone user about certain conditions that persist. For example a “normal” dial tone indicates that the telephone is connected and the user can make a call, while alternative dial tones may include, for example, a “message waiting” dial-tone indicating that the user has a new voice-mail message waiting to be listened to, or other “special” dial-tones indicating other conditions that may arise from time to time. For example, a user may be able to create or activate certain special rules for forwarding calls or messages, and such may be indicated by a “special” dial-tone. The special dial tone indicates that an unconditional forwarding rule is active, i.e. no incoming calls will be presented to the terminal, as they are unconditionally forwarded, to e.g. voice mail or a third number.
In traditional analogue public switched telephone networks (PSTNs) having fixed lines, the dial tone is triggered by an appropriate electrical signal fed to the telephone. In today's IP-based telecommunications systems, for a network that replaces a PSTN the dial tone information is handled by a PSTN Emulation Subsystem (PES) (see ETSI TS 183 043 “Telecommunications and Internet Converge Services and Protocols for Advanced Networks (TISPAN); IMS based PSTN/ISDN Emulation Stage 3 specification”). However, mobile terminals do not generate a dial tone. This is because the number is dialled ‘en block’, so the dial tone information can not be presented to the end user as audible information. Moreover, particularly with the advent of the IP Multimedia Subsystem (IMS) developed by the 3rd Generation Project Partnership (3GPP), the communication endpoint could be another type of user equipment (UE) terminal such as a personal computer (so-called PC clients) and PC Soft client terminals. Such terminals also do not generate a dial tone, and so networks do not currently provide dial-tone information to these user terminals. As a result the user is not made aware of the information that is conveyed in the dial tone, such as the existence of a new voice-mail message or other special conditions.
The present invention has been conceived with the above limitations in mind.